1. Field of the Invention
The present invention relates to a reservoir tank attached to an axle driving system in which a hydrostatic transmission (hereafter referred to as HST), an axle, and a drive train for connecting the HST and the axle for driving are housed in a common housing.
2. Related Art
Conventionally, a housing that houses an HST is filled with hydraulic oil that is also used as lubricating oil. A temperature of the hydraulic oil is increased by driving the HST. The increase in temperature of the hydraulic oil results in an increase in its volume. In order to receive the increase in the volume, a technique of providing a reservoir tank on an outside of the housing or forming space having a volume corresponding to the increase within the housing to form a reservoir room is known.
For example, there is a technique disclosed in U.S. Pat. No. 4,987,796 or U.S. Pat. No. 5,440,951.
However, an axle driving apparatus that utilizes a reservoir tank structure requires additional space, a mounting member for mounting the reservoir tank, and piping for connecting the reservoir tank and the housing. In addition, the number of man-hours required for assembly increases, the reservoir tank is difficult to handle, and cost increases.
By positioning the reservoir tank at an upper portion of the housing, a vertical length of the housing increases to inhibit miniaturization of the axle driving system and an air layer is created in the housing to cause air to be swallowed in oil when the oil within the housing is stirred. If this oil is charged into a closed circuit of the HST as the hydraulic oil, volume efficiency of the HST is reduced, which may generate noise or reduce durability.
Further, it is difficult to integrally form the reservoir tank at the upper portion of the housing for a lawn tractor having a rear discharge method, because a chute passes above the axle driving system.
According to the present invention, a tubular reservoir tank is mounted to stand on an upper face of an upper wall-face of a housing that houses an HST including a hydraulic pump and a hydraulic motor. The reservoir tank communicates with an oil reservoir within the housing. Therefore, it is possible to easily mount the reservoir tank by a simple structure, to form the reservoir tank from low-priced members, and to reduce cost.
The reservoir tank is formed of a tubular member. Therefore, if there is a member such as a chute that is related to the vehicle main machine above the housing, it is possible to mount the reservoir tank by bending the reservoir tank. Therefore, it is possible to easily mount the reservoir tank by causing the reservoir tank to make way for the member that interferes with the reservoir tank, thereby increasing the number of applications in which the axle driving system may be used.
The housing is partitioned into a first room, housing the HST and a second room, housing an axle and a gear train for transmitting power from the hydraulic motor to the axle. The first and second rooms communicate with each other such that the oil with which both the rooms are filled can circulate between both the rooms. The reservoir tank is disposed on the second room. Therefore, it is possible to position a mounting portion of the reservoir tank in a high position, thereby easily purging air generated within the reservoir tank. Because the reservoir tank may be disposed in a position isolated from the pump shaft, it is possible to easily prevent the reservoir tank from interfering with a rotary member such as an input pulley or a cooling fan.
A communicating position connecting the first room and the second room allows oil to pass there between. A filter member for removing impurities included in oil is disposed in the communicating position. Therefore, it is possible to remove impurities included in the oil when the oil circulates between the first room and the second room due to the variation in volume of the respective rooms which occurs with a change in oil temperature or stirring by actuation action of the HST or rotation of a gear. The impurities can be removed by means of the filter member disposed in an oil hole for hydraulic oil of the HST, the oil within the first room can be cleaned, and durability of the HST can be further improved.
Because the filter member is formed of a magnet, the filter member can be formed at low cost and can be miniaturized. Therefore, limitations to a place where the filter member is disposed can be reduced, durability of the filter member is high, and the filter member can be cleaned easily.
A closed circuit is formed by providing an oil path to a center section to which a hydraulic pump and a hydraulic motor in the HST are mounted, an oil hole opening at the center section for supplying hydraulic oil to the closed circuit is connected to an oil filter disposed in an oil reservoir, and a magnet is disposed in the oil reservoir in a vicinity of the oil filter. Therefore, it is possible to cause the magnet to collect iron powder before it is drawn into the oil hole and to easily remove the harmful iron powder before it enters the closed circuit of the HST.
The magnet is disposed such that the magnet acts on the hydraulic oil after passing through the oil filter and before entering the oil hole. Therefore, if there is extremely fine iron powder that has passed through the oil filter, the iron powder can be collected by the magnet and prevented from entering the closed circuit of the HST, thereby increasing life of the HST. Because only small iron powder is collected by the magnet, an amount of iron powder collected by the magnet is small even after use of the magnet for a long term and frequency of maintenance can be reduced.